I suspect that leaf springs are useful not only because
the designer liked whatever characteristcs leaf springs
are good at (I don't really know),
They're cheap, easy to find and easy to modify -- add or remove
leaves to get your desired spring rate. They're also easy to
tune for ride height by adding or removing spacer blocks.
but additionally they would
keep the hoodline low - no need for strut towers or spring
cups, etc.
As an aside, anyone know why the old design using a xverse
leaf spring as the upper suspension arm (a la the BRM V-16 (?))
was abandoned? I figure that it might have been because the
upper arm would be more easily deflected than a real A-arm,
but the design is certainly appealing in it's simplistic elegance...
The biggest problem is geometric. Consider a leaf spring, basically
a bow (as in "and arrow") made of several layers of metal. The
linear distance between the two ends changes as the spring flexes;
you can't get around that. This is why leaf-sprung cars usually have
spring shackles at the rear, typically a pair of bolts with metal
plates forming a rectangle that pivots at both ends. The idea is
that as the spring elongates or shortens under suspension motion,
the free end pivots to compensate for this flex.
This can cause headaches when you try to design a camber curve around
this characteristic. Basically, if you have the spring arched at any
degree other than fully flat at static ride height, you get positive
camber (that is, the top of the wheel tilts outward) at the outside
wheel under body roll. (The same geometric problem causes rear-steer
effects in most cars with ordinary longitudinal leaf springs as well;
the cheapest solution is to fix the axle to the center of the spring,
leave only the rear end of the spring free to adjust for length, and
to try to compensate for the length change in the front half of the
spring as best you can.)
Basically, as cars got more expensive and faster, it became worth
everyone's while to design suspensions around ideal performance
rather than around a workable performance compromise. For racing
cars, the ideal performance is obtained with a dual A-arm setup
where the bottom arm is longer than the top, and both are as long
as possible.
ed 'give me torsion bars or give me death' devinney
--Scott "Try trail-braking in a 356 and get BOTH" Fisher
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